The present disclosure relates to a light emitting element (particularly, a surface emission laser element sometimes called vertical resonator laser or VCSEL).
Generally in a light emitting element configured from a surface emission laser element, laser oscillation occurs by causing laser light to resonate between two light reflection layers (Distributed Bragg Reflector layers, DBR layers). In a surface emission laser element having a structure in which an n-type GaN-based compound semiconductor, an active layer (light emitting layer) configured from a GaN-based compound semiconductor and a p-type GaN-based compound semiconductor are stacked, generally a second electrode made of a transparent conductive material is formed on a p-type compound semiconductor layer and a second light reflection layer configured from a stacked structure of an insulating material is formed on the second electrode. Further, a first electrode and a first light reflection layer configured from a stacked structure of an insulating material are formed on an n-type compound semiconductor layer. It is to be noted that, for the convenience of description, an axial line passing the center of a resonator formed from two light reflection layers is referred to as Z axis, and a virtual plane orthogonal to the Z axis is referred to as XY plane.
Incidentally, in a surface emission laser element, in order to control the flow path (current injection region) of current that flows between the first electrode and the second electrode, a current non-injection region is formed so as to surround a current injection region.
In a surface emission laser element configured from a GaAs-based compound semiconductor, the current non-injection region surrounding the current injection region can be formed by oxidizing the active layer from the outside along the XY plane. The refractive index decreases in the oxidized region of the active layer (current non-injection region) in comparison with a region that is not oxidized (current injection region). As a result, the optical path length (represented by a product of a refractive index and a physical distance) of the resonator in the current non-injection region becomes shorter than that in the current injection region. This gives rise to a kind of “lens effect” and brings about an action for confining laser light at a central portion of the surface emission laser element. Since light generally tends to spread by a diffraction effect, laser light that reciprocates in the resonator gradually dissipates to the outside of the resonator (diffraction loss), and this has a bad influence such as increase of threshold value current or the like. However, since the lens effect compensates for the diffraction loss, increase of threshold value current or the like can be suppressed.
However, in a surface emission laser element configured from a GaN-based compound semiconductor, it is difficult to oxidize the active layer from the outside (from a lateral direction) along the XY plane from the characteristics of the material. Therefore, an insulating layer made of SiO2 and having an opening is formed on the p-type compound semiconductor layer, and a second electrode made of a transparent conductive material is formed over a region from the second compound semiconductor layer exposed to the bottom of the opening to the insulating layer. Further, the second light reflection layer configured from a stacked structure of an insulating material is formed on the second electrode (for example, refer to JP 2011-151364A). The current non-injection region is formed by forming the insulating layer in this manner. Further, a portion of the compound semiconductor layer provided on the insulating layer and positioned in the opening is utilized as the current injection region.